For preventing the light beam from being leaked out through a lateral surface of an illuminated keyboard, a reflecting plate and an upper wiring plate of the conventionally illuminated keyboard are usually adhered to each other. FIG. 1 is a schematic cross-sectional view illustrating a conventional illuminated keyboard. As shown in FIG. 1, the conventional illuminated keyboard 10 comprises a light source L, a key structure 11, and a backlight membrane switch module 12. The backlight membrane switch module 12 is disposed under the key structure 11. The light source L is located at a side of the backlight membrane switch module 12.
The backlight membrane switch module 12 comprises an upper wiring plate 13, a partition plate 14, a lower wiring plate 15, a light guide plate 16, and a reflecting plate 17. The upper wiring plate 13 comprises an upper circuit layer 131. The lower wiring plate 15 comprises a lower circuit layer 151. The partition plate 14 comprises a perforation 141. The partition plate 14 is arranged between the upper wiring plate 13 and the lower wiring plate 15 for separating the upper wiring plate 13 from the lower wiring plate 15. As the key structure 11 is depressed by the user, the upper circuit layer 131 of the upper wiring plate 13 is penetrated through the perforation 141 of the partition plate 14 and contacted with the lower circuit layer 151 of the lower wiring plate 15. Consequently, a key signal is correspondingly generated.
The light guide plate 16 is disposed under the lower wiring plate 15. Moreover, the light guide plate 16 is located at a side of the light source L for transferring the light beam. The reflecting plate 17 is disposed under the light guide plate 16 for reflecting the portion of the light beam that is outputted from the bottom of the light guide plate 16. Consequently, the light utilization of the light beam from the light source L is enhanced. The reflecting plate 17 is an opaque substrate, or the reflecting plate 17 is formed by coating an opaque material on a surface of a light-transmissible substrate.
For preventing the light beam which is transferred within the light guide plate 16 from being leaked out through a lateral surface of the light guide plate 16, an edge region of the upper wiring plate 13 and an edge region of the reflecting plate 17 of the conventional illuminated keyboard 10 are attached on each other. Since the lateral surface of the light guide plate 16 is enclosed by the reflecting plate 17, the light beam is prevented from being leaked out through the lateral surface of the light guide plate 16. Consequently, the problem of causing light leakage through the lateral surface of the light guide plate 16 will be eliminated.
However, since the edge region of the upper wiring plate 13 and the edge region of the reflecting plate 17 are attached each other, the overall volume of the conventional illuminated keyboard 10 is increased. For a small-sized keyboard (e.g. a keyboard of a notebook computer), since the inner space is insufficient or the position of the key structure is close to the edge region of the upper wiring plate 13, the distance between the edge region of the upper wiring plate 13 and the circuit layer printed on the upper wiring plate 13 is usually very small. Under this circumstance, the edge region of the upper wiring plate 13 and the edge region of the reflecting plate 17 of the conventional illuminated keyboard 10 fail to be successfully attached on each other. In other words, the conventional illuminated keyboard 10 still has the light leakage problem.
Therefore, there is a need of providing an improved illuminated keyboard in order to overcome the above drawbacks.